1. Field of the Invention
The present invention relates to an inkjet recording apparatus and an inkjet recording system that can form high-quality images on various types of recording media.
2. Description of the Related Art
There are conventional inkjet recording apparatuses that can improve image quality in inkjet recording operations by using a plurality of inks having different color material densities. For example, there is an inkjet recording apparatus that uses light inks having lower color material densities, such as light yellow (light Y, LY), light magenta (light M, LM), and light cyan (light C, LC), in addition to four fundamental colors of Y, M, C, and K. It is generally known that graininess of recorded images can be reduced by positively using these light inks when highlight portions are printed.
Further, there is a conventional method capable of forming a high-quality image that is excellent in color developing properties as well as in gradation characteristics by determining an optimum combination of inks that are selectable from a plurality of predetermined inks having different color material densities according to the type of a recording medium to be used. The inkjet recording apparatuses that perform recording with a plurality of inks different in color material density perform important roles in improving the quality of recorded images.
On the other hand, recording of images using pigment inks that have excellent image fastness properties for a printed product compared to dye inks is desired. There are various types of recording media, such as plain papers represented by PPC sheets, coated papers including an ink receptive layer provided on a substrate (e.g., a wood-free sheet or a film), CD/DVD or comparable disks, OHP sheets, and postcards. Further, the coated papers that are currently available in the market to provide high image quality and high product quality can provide a wide variety of product types in the feel of material, from glossy papers having a mirror surface excellent in glossiness to mat papers having a mat surface.
The issue to be solved to attain high-quality images in the inkjet recording apparatuses using pigment inks differs depending on the type of a recording medium to be used. For example, a method discussed in U.S. Pat. No. 6,670,409 can improve not only color developing properties of the plain papers but also scuff resistances of the coated papers. In general, the plain papers are inferior to the coated papers in color developing properties. The coated papers are inferior to the plain papers in scuff resistance. According to the method discussed in U.S. Pat. No. 6,670,409, dark inks are mainly used for the plain papers and light inks containing polymers are mainly used for the coated papers.
However, according to the method discussed in U.S. Pat. No. 6,670,409, requirements of both high color developing properties for the mat papers and high glossiness for the glossy papers may not be satisfied simultaneously. More specifically, it is useful to use dark inks for the mat papers having excellent ink absorbency to obtain adequate color developing properties. However, if dark inks are used for the glossy papers having poor ink absorbency, residual color materials tend to form an undulated surface on a recording medium.
FIG. 1A illustrates two ink dots, each of which has been discharged from a recording head and impacted on a recording medium. As understood from the illustration in FIG. 1A, the height of a single ink dot becomes higher as the color material density of the used pigment ink is higher. The height difference between the respective ink dots decreases glossiness of a recorded image. To solve this issue, it may be useful to additionally coat the undulated surface of the recording medium with, for example, a transparent ink layer to reduce the roughness and realize sufficient glossiness. However, the consumption amount of the transparent ink may increase significantly.